Solid state electronic devices are employed in a wide range of manufactured products. The devices are found in aircraft, automobiles, computers, industrial control systems, military systems, home appliances and many other applications. Within this wide range of applications, there is a correspondingly wide range of environmental conditions in which the devices must operate successfully. In particular, there is a wide range of ambient temperatures in which these devices must operate.
In many instances, performance characteristics of electronic devices are temperature dependent. As a result of this temperature dependency, many devices are designed to produce optimum performance within a predefined range of operating temperatures.
Most solid state electronic devices produce heat during their operation. Many of these devices produce varying amounts of heat depending on the functions which they are performing at any moment.
Typically, this varying amount of heat energy is carried away from the device by convection currents of ambient air. For devices which generate large amounts of heat, metallic heat sinks are employed to remove excess heat energy through thermal conduction.
These conventional temperature control measures are usually satisfactory when the devices are operating in ambient conditions that have a narrow range of temperatures. For example, room temperature in an air-conditioned office setting would present ambient temperature conditions which vary no more that a few degrees.
Workers in the prior art have found that these conventional temperature control measures are not sufficient in circumstance where electronic devices are exposed to wide ranging ambient temperature. For example a device used in an aircraft standing on a tarmac runway may be exposed to temperatures in excess 50 .degree. C. That same device may be exposed to temperature as low as -50 .degree. C. an hour later when the aircraft is flying at 11,000 meters.
In these extremely wide ranging temperature conditions there is often a need to provide a more sophisticated temperature control for electronic devices. Designers must provide measures for both retaining and removing heat in a device, depending on the ambient temperature in which the device is operating. In other words, devices must be assembled onto mechanisms which have a heat dissipation capability that is variable as a function of ambient temperatures.
This need for sophisticated temperature control has been recognized and addressed in the prior art in a number of ways.
For example, there are thermo-electric cooling devices which employ the so-called Peltier effect. The devices can provide accurate control of operating temperature of a single device. However, this temperature control is not achieved without deleterious side effects. Peltier coolers have very low efficiencies. When a Peltier cooler is used to cool a typical 1/4watt laser there is need for power input of about 4 watts into the cooler. Consequently, an assembly of electronic devices which are cooled with Peltier coolers presents an overall cooling requirement that may be as much as sixteen times as great that needed for the actual electronic devices.
Also, within the prior art, considerable effort has been directed to enhancing the temperature control capabilities of enclosure and support racks for electronic device assemblies. Some examples of this design effort is found in the following U.S. Patents.
In U.S. Pat. No. 5,894,407 (Aakalu et al.), issued Apr. 13, 1999, and U.S. Pat. No. 5,769,159 (Yun), issued Jun. 23, 1998, enclosures for electronic assemblies are provided with air passageways which are adjustable in size. The size adjustment takes place passively and as a function of the temperature of air flowing through the passageways. These systems are effective in controlling an overall temperature of an entire electronics assembly. They are not, however, capable of controlling the temperature of a single device or a subset of devices at a temperature different from other devices in the entire assembly.
In U.S. Pat. No. 5,101,320 (Bhargava et al.), issued Mar. 31, 1992, an enclosure is constructed with a series of parallel supports with air-flow channels between each support. The airflow channels are adapted to remain closed if there is no circuit board on an adjacent support. This arrangement provides enhanced cooling for every circuit board in an enclosure. But, it does not provide for any individualized cooling for any particular circuit board or any particular sub-set of electronic devices.
In U.S. Pat. No. 4,739,444 (Zushi et al.), issued Apr. 19, 1988, an enclosure is structured so that air cooling channels are provided with flow restrictors. Each flow restrictor is a plate with a unique pattern of air passage holes. Each flow restrictor is produced to optimize air flow through its corresponding channel on the basis of the geometry and air-flow resistance of the electronic devices that are adjacent that channel. This arrangement provides individualized cooling control for particular circuit boards, but the system cannot accommodate any rearrangement or changes in the nature of the circuit boards which are placed in the enclosure. In other words, the enclosure design does not readily accommodate upgrades of an electronic system.
Present day electronic systems are manufactured and sold in a very competitive economic climate. Consequently, there is a need to provide electronic assemblies in cabinets and enclosures which can be produced at low cost. This translates into a need for enclosures that is made in a universal style which accommodates a wide combination of electronic devices. Additionally, these low cost universal enclosures must readily accommodate upgrades and modifications of the electronic systems.
Heretofore, there has been no enclosure design which has provided this desirable universality along with individualized cooling control capability. It is important, therefore to devise system for supporting and accurately maintaining temperature of a wide range of combinations of electronic devices in low cost enclosures.
The present invention meets these goals.